In the current state of the technique, the preparation of anhydrous ethanol from aqueous solutions first involves producing an ethanol/water mixture containing 95 vol. % of ethanol, the ethanol/water mixture making up an azeotrope containing 95.6 wt. % of ethanol at 0.1 MPa. This operation involving a distillation process is a highly energy-consuming operation. For example, starting from an aqueous solution containing about 10 vol. % of ethanol, approximately 180 kg steam per hectoliter of ethanol are necessary to obtain this mixture.
After this first distillation stage, several options can be considered for drying the aqueous ethanol solution from about 95 vol. % to at least 99.8 vol. %:    azeotropic distillation in the presence of a third body (benzene or cyclohexane for example),    membrane pervaporation,    molecular sieve adsorption.
The option using azeotropic distillation in the presence of benzene or cyclohexane involves a high energy expenditure since it requires about 110 kg steam and about 1.3 kWh per hectoliter of alcohol. Furthermore, the toxicity of benzene and cyclohexane is a major drawback of this process.
The option using membrane pervaporation is clearly more interesting as regards energy expenditure since it consumes only about 30 kg steam and about 4.5 kWh per hectoliter of alcohol produced.
Molecular sieve adsorption is a moderately energy-consuming operation that requires about 30 to 60 kg steam and about 2 to 3 kWh per hectoliter of alcohol in the case of a PSA (Pressure Swing Adsorption) process with adsorption in the vapour phase.
Alcohols being generally partly soluble in most liquids, it is obvious that any contacting operation between an aqueous phase containing an alcohol and another liquid phase containing none induces extraction of a non-zero fraction of the alcohol from the aqueous phase to the other liquid phase. U.S. Pat. No. 4,455,198 and U.S. Pat. No. 4,346,241 describe methods of preparing anhydrous ethanol wherein a liquid-liquid extraction is carried out with cyclic ketones or alcohols on the one hand, or amines on the other hand.
The possibility of extracting ethanol with gasoline has already been considered in the past, as mentioned in U.S. Pat. No. 4,297,172. In the temperature range studied and with the gasoline type used, extraction is relatively difficult so that it is considered only from a highly alcohol-enriched aqueous phase. The method described in this patent application allows to do without the extremely energy-consuming stage of azeotropic distillation that is commonly carried out. In the first stage of this process, the ethanol-containing aqueous phase is however subjected to distillation in order to concentrate the ethanol and to obtain a distillation comprising at least 75 wt. % of ethanol. This essential first concentration stage makes the process still too energy-consuming a method. Furthermore, the final yields are relatively low since this method allows to extract only 5 to 17 wt. % of ethanol.